Catalytic conversion of hydrocarbons



Patented May 2, 1950 CATALYTIC CONVERSION OF HYDROCARBONS i Forrest H. Blanding, Elizabeth, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application June 20, 1947, Serial No. 755,909

2 Claims. (01. 196--49) 1 This invention relates to the catalytic cracking of hydrocarbons.

In the cracking of hydrocarbons it has now'been found that when cracking gas oils in the presence of synthetic silica alumina gel catalyst, there is a difference in the octane number of the gasoline produced when using high boiling gas oil and v low boiling gas oil. When cracking a high boiling gas oil the gasoline produced has a substantially lower octane number than when cracking a low boiling gas oil. 1

When cracking high boiling gas oils with acid treated clay catalysts the octane number of the gasoline produced is also lower than with the low boiling gas oil but the difference is not as'great as when using the synthetic catalyst.

crude oil source can be varied from about 450 to 750 F. and at similar operating conditions and conversion levels the gasoline produced will have octane numbers varying only about 0.1 to 0.3 7 number.

On the other hand if the average boiling level of the feed stock is further increased slightly to about 850 F. an abrupt drop of octane numbers, to 90 octane number gasoline, will be obtained. The abrupt transition in octane level obtained is an unexepected and unusual phenomenon.

It has been found that when cracking similar gas oils with natural clay cracking catalysts, such as acid treated bentonltes, that a much smaller change in octane level is obtained when the average feed stock boiling level varies between about 750 F. and 850 F. Thus, where with the use of synthetic silica alumina catalyst a gasoline of almost 3 octane numbers higher is obtained than with the acid treated clay or bentonite catalyst from a 600 F. average boiling point feed, a 0.4

, higher octane number gasoline is obtained with the clay catalyst than with the synthetic catalyst for an 850 F. average boiling pointfeed.

. gas oil, and that this material i relatively less harmful when cracking with a natural clay catalyst.

From the above 'it will be apparent that even though the synthetic, catalyst is more expensive than clay catalyst there is an advantage for using it on feed stocks boiling below about 800 F. due in part to the octane advantage. The synthetic and clay catalysts are closely competitive economically and if the octane advantage for the synthetic catalyst is removed, clay has the advantage of lower cost. As the acid treated clay catalyst gives better octane number gasoline for feed stocks boiling above about 800 R, an economical advantage will be obtained on the basis of octane credit by cracking feed stocks boiling below about 800 F. with synthetic catalyst and cracking feed stocks boiling above about 800 F. with the clay catalyst.

Furthermore, by using the lower boiling and relatively clean feed stocks with synthetic catalyst there will be less contamination of this more expensive catalyst, whereas, the cheaper natural catalyst may be used at a higher replacement rate for the more contaminated higher boiling feed stocks.

According to one form of my invention, then, a

relatively narrow boiling feed stock boiling between about 430 F. and 800 F. and having an 80%20% distillation temperature range preferably of not more than about 200 F. is cracked over a synthetic silica alumina catalyst to give high octane gasoline and the fraction boiling above about 800 F., either narrow boiling or wide boiling, is cracked in a separate reactor or unit over a natural catalyst or other relatively cheap catalyst to produce as high or a higher octane gasoline product than is produced in cracking the narrow boiling stock above described.

According to another form of my invention gas oils are carefully fractionated to eliminate material boiling above about 800 F. when the gas oil is feed stock to a catalytic cracking unit employing the synthetic catalyst.

With the use of my invention there should result substantially better overall product per unit operating cost in certain refinery situations.

In the drawing:

'The figure represents one form of apparatus which may be used in carrying out my invention.

Referring now to the drawing the reference character l0 designates a iractionating tower into which hydrocarbon feed is introduced through line l2. The hydrocarbon feed stock may comprise a wide cut gas oil, crude petroleum oil, a reduced crude petroleum oil or other suitable hydrocarbon stock which is to be treated. In the fractionating tower It the hydrocarbon feed is fractionated into a bottoms fraction withdrawn through line I4, a gas oil fraction withdrawn as (Lalculated by subtracting the temperature in F. at which 20% of the fraction distills off from the tempera.- ture in F. at which 8.0% of the fraction distills off.

a side stream through line It and overhead vapors withdrawn through line; I 8.

Preferably the hydrocarbon'cil being introduced into iractionating tower I9 is vaporized before it is introduced into the tower and desired heating means may also be provided in hydrocarbons pass overhead through line 25 and may be further treated for the recovery of normally liquid hydrocarbons orthey may be utilized as such. The liquid hydrocarbons containing gasoline constituents-are withdrawn through line 28 and to storage. Preferably'a portion of the liquid hydrocarbons'are passed throughline 32 by pumped into the upper portion of the fractionating tower Iii-as reflux liquid.

According to my invention I have found that improved octane number gasoline may be obtained by eliminating high boiling constituents from gas oil :feed which is to be cataiyi aaily cracked. The-gas oil fraction which is-withdrawn from trap-out tray :35 from the tower is and through line It; and in one case has an tial boiling-point of about430 F. and-a final boiling point of about 800 F. The average'boiling point of this feed stock is about 625 F. The average boiling point of the feed stock is obtained as the average of the temperatures at-which and 8%% respectively, of the feed stock is distilled over in a batch distillation still having a distiiiation efiiciency as good as or better than the equivalent of plates operated at 5/1 reflux ratio.

The lower boiling feed stock comprising the gas oil withdrawn through line .lii is catalytically cracked in one vessel :01 reactor and the higher boiling fraction withdrawn throughline Hi from the bottom of the fractionatingtower id is catalytically cracked in a second vessel orreactor. The cracking Of the lower boiling gas oil fraction will be first described.

' The gas oil fraction withdrawn through line l 5 may be vaporized and the vapors introduced-into cylindrical reactor 33. Instead of vaporizing the I gas oil fraction it may be partly preheated by heat exchange the process and the partly preheated I oil then mixed with a sufiicient amount of hot grid member 33 arranged in the bottom poi .-;on I

of the reactor vessel 38. Preferably grid member 58 is circular and arranged concentrically with the vessel 38 in the lower portion thereof. The grid member :8 acts to evenly distribute the powdered catalyst and the oil vapors across the area of the reactor vessel 38. Instead of adding the catalyst particles and hydrocarbon feed together as a mixture the catalyst and hydrocarbon feed may be separately introduced into the vessel 38.

The va- The overhead vapors are passed The temperature during the cracking of hydrocarbons may range from about 150 F. to 1050 F.

"and preferably about "925F; to 1000" F. in the catalytic cracking of hydrocarbons to form high anti-knock gasoline. The catalyst to be used in cracking the lower boiling gas oil fraction comprises asynthetically prepared silica alumina gel.

The catalyst is preferably in finely divided form having a particle size between about 200 and 400 standard mesh and containing less than about 30% by weight of material smaller than about 2i) microns. The temperature of the hot regenerated particles in line 52 is about 999 to 1100 F.

Returning now to the reaction vessel 33 the hydrocarbon feed and'catalyst particles are introduced into thevessel 38 and the superficial velocity of the u'pfiowing vapors is selected-to "maintain the solid particles in a dense --dry 'lyst particles.

ifiuidized liquid-simulating turbulent condition as shown at 52 and having a level as indicatedat 54. The superficial velocity is that velocity measured with the vessel empty andmay be between about 0.5-feet per second to 2.0 feet per second. Under these conditions and using the 200 to 400 mesh synthetic silica alumina catalyst material above described the density of the fluidized mixture in the reactor 38 may vary between about 15 pounds per cubic foot and 35 pounds per cubic foot.

Above'the dense mixture is a dilute phase or dilute suspension 55 comprising vaporous reaction products containing some entrained cata- The upperportion of the reaction vessel 38 designated by the reference character 56 comprises a settling section in which the catalyst particles fall back into the dense mixture 52 so that only a dilute suspension or dispersed phase 56 is superimposed above the dense mixture 52. The density of the dilute suspensionin the space 56 may'vary between about .005 pound per cubic foot to 1 pound per'cubic foot when using the silica alumina catalyst above referred The vaporous reaction products containing some entrained catalyst'particles leave the-dilute phase section 56 and ar passed into separation means 58'through inlet line 62 'for removing or separating most of the solid particles from the vaporous reaction products leaving the space 56. The separation means is shown as a cyclone separator arranged in the upper portion of the reaction vessel 38 but other forms of separation devices may be used as for example Multiclones.

If'desired more than one separating stage may be used'in series. It is'not essential that the separating means'58 be inside thereaction vessel 38 as the separating means maybe arranged outside of th reactor 38.

The separated solid particles collect in the separation means58 and are returned to ,the dense bed or mixture 52 through dip pipe 64. The vaporous reaction products'substantially free of catalystiparticles lDfi-SS overhead through line 66 ,matically shown at 36.

gnaw-291 the distribution gridmember48 and between the i 'conicalinlet member tfiandlthe inner wall of the reaction vessel .38. WThe .partially spent catalyst particles are at a temperature of about 750 F.

to 1050 F.

. Stripping gas suchas steam is introduced into .the. bottom. portion of the. stripping zone .72

throughone or more lines I4 .for removing hydrocarbon vapors entrained with the withdrawn spent catalyst. The superficial velocity of the stripping gas in the stripping zone is about 0.3 .foot per second to2 feet per second. The density .of the fiuidizedmixture in the stripping zone 12 .is. about the same as thedensity of the dense mixture in the vessel 38 but it may be higher or lower.

In order to maintain the catalyst particles in a fluidized condition as they are withdrawn from the vessel 38, fluidizing gas is introduced through one or more lines 16 intothe densemixtur in the bottom of the vessel 38. The dense fluidized and stripped catalyst particles are passed into a stand-pipe 'I8having a control valve 82 for controlling the rate of withdrawal of catalyst particles from the reaction vessel 38. The fluidized solids in the reaction vessel 33 and in the standpipe 18 produce a hydrostatic pressure at the.base of the standpipe is which is used for passing the catalyst particles through the system. -The spent particles leaving the standpipe I8 are mixed with a regenerating gas such as. air or other oxygen-containing gas introduced through'line 84'to make a less dense mixture or' suspension and this suspension is passed through a regeneration zone diagram- The regenerated catalyst particles at a regeneration temperature are withdrawn andpassed through line 32 and introduced into the reaction vessel 38 as above described. ,The hot regeneration gases are Withdrawn through line 88.

' While I have shown the regeneration zone or vessel diagrammatically it is to be understood that in fluid operations the regeneration will be =carried out in a mannersimilar to that described .above in. connection with the reaction vessel 38. That is, the particles undergoing regeneration are maintained asa dense fluidized mixture with a dilute or dispersed phase superimposed thereabove. The hot regenerated catalyst particles tower 68 the vaporous reaction products are trace.

tionated to separate condensate oil whichis withi drawn through line 92 from the bottom of the tower. A gas oil is withdrawn from trap-out tray 94 arranged above the inlet line 66 to the tower S8 and passes through line 96 to storage. j

The hot vaporous reaction products on being introduced into the bottom of the second fractionating tower 68 are cooled and higher boiling constituents are condensed. These vaporous; re-

action products contain some entrained catalyst particles and these particles are recovered in the condensate oil as a slurry. The catalyst particles maybe recovered from the condensate oil by filtering, settling or other separating operations.

- from the vapors.

G The .vaporsv passhoverhead from the tower 68 through line 98 and arepassed through condenser IM to condense normally liquid hydrocarbons containing .gasoline..constituents. The cooled mixture .isintroduced into separator. I04 for separating normallygaseous hydrocarbons which are withdrawn overhead through valved line I116. The normally. liquid hydrocarbons comprising .highv :antiknock gasoline are withdrawn from the bottomof separator I04 through line I68 and passedto storage. The gasoline is preferably. further. treated with sulfuric acid or clay to improve thequality of the gasoline. As these finishing treatments are old in the art it is not believed necessary to further describe them.

At least a portion of the liquid hydrocarbons withdrawn through line I08 is passed through line H2 by pump II into the upper portion of the second fractionation tower 68 as reflux liq uid. Instead of using the reflux liquid cooling means may be provided in the upper portion of the tower 63;

' Returning now to the higher boiling fraction which is withdrawn from the first fractionating tower It! through line I4 the fraction may be partly preheated and then mixed with hot regenerated catalyst from line I I6, a suificient amount of catalyst being used-to vaporize the oil and raise it to'cracking temperature; According to my invention the fraction withdrawn through line H has an average boiling point above about 800 .F. and for cracking this higher boiling stock I use a natural cracking catalyst such as powdered acid treated bentonite clay. I have found that, as high or higher octane gasoline is produced when crackin the higher boiling stock with a cheap natural clay catalyst than when cracking the same stock with the more expensive synthetically prepared silica alumina gel catalyst.

The mixture of the higher boiling fraction and the clay catalyst is passed through line IIS and into conical inlet member I22 provided with a perforated grid member I 24 arranged in the bottom portion of the second reaction vessel I25. The powdered clay catalyst has about the same particle size distribution as the synthetic cata lyst above described in the first cracking step. The velocity of the upflowing vapors in the second reaction vessel I26 is selected to maintain azdense fluidized-bedor mixture I28 of'catalyst particles having a level indicated at I32. The velocity of the upfiowing vapors and the density of the bed or mixture I28 is substantially the .same as that described above in connection with the first reaction vessel 38. Above the dense bed or mixture is superimposed a dilute or disperse phase I34. The vaporous reaction products passing upwardly are introduced into separating means I36 through inlet I38 for separatin entrained catalyst particles The separated particles accumulate in the separating means I36 and are returned through dip leg I42 to the dense bed or mixture I28. The separated vapors pass over- Ehead through line I44 and may be passed through valved line I46 to the second fractionating tower 68 above described or they may be passed through valved line I48 to the bottom portion of a third fractionating tower I52 presently to be described in greater detail.

Similar to the operation described in connection with reaction vessel 38 the spent or partly deactivated catalyst particles are withdrawn fromthe bottom portion of the spent reaction vessel diagrammatically shown at I12.

vessel E25 and passed into the annular stripping zone or section I54 into which stripping gas is introduced through lines I56. The catalyst particles in the bottom portion of the vessel I26 are maintained in a fluidized condition by the introduction of fluidizing gas through one or more lines I58.

The stripped catalyst particles are then introduced into the upper portion of a second standpipe 562 provided with one or more fluidizing lines I64 for maintaining the particles in a fluidized condition in the standpipe I62. The fluidized mixture I28 and the fluidized mixture in the standpipe 562 produced a hydrostatic pressure at the base of the standpipe I62 which is used for passing the catalyst particles through the regeneration system. The spent catalyst particles pass through the control valve I66 and are mixed with a regenerating gas introduced through line I68 to form a less dense mixture or suspension which is passed to a second regeneration zone or The hot regenerated catalyst particles are withdrawn and passed through line I I6 for introduction into the second reaction vessel I26 and hot regeneration I gases are withdrawn and passed through line $74.

As above pointed out in connection with the regeneration zone 86 the regeneration zone or vessel I12 may comprise a vessel similar to reaction vessels 38 and I26. That is, the catalyst 3 particles undergoing regeneration are maintained as a dense fluidized mixture having a level with a dilute suspension superimposed thereabove. The regeneration gases pass overhead from the regeneration zone and are passed through a separating means to reecover entrained catalyst particles from the regeneration gases. Heat may be recovered from the hot regeneration gases as above pointed out in the discussion of the first 8 I16. This condensate oil contains catalyst particles which were entrained with the vapors and the particles may be recovered from the slurry by settling, filtering, etc. The gas oil is withdrawn from trap-out tray I18 through line I82.

The vapors pass overhead, pass through line I84, through condenser I66 and into separator I88. The gases are withdrawn overhead through line I92 and the normally liquid hydrocarbons containing high anti-knock gasoline are withdrawn through line I94. At least part of the gasoline-containing fraction withdrawn through line IE4 is preferably blended with at least part of the gasoline fraction withdrawn through line I08 from the second fractionating tower 68. If desired, at least part of the virgin gasoline withdrawn through line 28 from the first tower I0 may also be blended with the mixture of the gasoline fractions just described.

To provide reflux for the third fractionating tower I52 at least a portion of the liquid hydrocarbons from line I94 is passed through line I96 by pump I98 into the upper portion of the tower. Instead of using reflux liquid, cooling means may be provided in the upper portion of the fractionating tower I52.

In the catalytic cracking in the second reaction vessel I26 the temperature may range from about 750 F. to 1050 F. and preferably about 925 F. to 1000 F. in the catalytic cracking step to form high anti-knock gasoline.

From cracking data I have noted that the octane number of the gasoline drops off precipitously when the feed stock average boiling point is raised from about 700 F. to about 800 F. when using the synthetic catalyst and that with a feed stock average boiling point above about 800 F., the octane number continues to drop off at a very moderate rate. Using acid treated regeneration zone 86. 40 bentonite clay as the catalyst and when the feed The hot regenerated catalyst particles are stock average boiling range is below about 800 F. preferably withdrawn from the bottom portion or 850 F., the initial octane number of the gasoof the regeneration zone as a dense fluidized line is not as high as the octane number of the mixture. In both regeneration steps stripping gasoline produced on a similar stock as above degas may be used for removing oxygen or other scribed using the synthetic catalyst, but the oxidizing gases from the regenerated particles. octane number of the gasoline does not fall ofi Returning now to the third fractionating tower nearly as fast when the average boiling point of I52. the reaction products from the second rethe feed stock is above about 800 F. or 850 F. action zone or vessel I26 are fractionated to The following TableI lists the octane numbers separate a condensate oil which is withdrawn produced when cracking various petroleum oils from the bottom of the tower I52 through line of difierent average boiling points.

Table I Petroleum 5 I Boiling Octane Num- 011 Av. Boil- Reactor Range, ber CFR- Yield of 10# Operation Experiment 111g Point, Conversion Operating No No 80%+20% 20?,nggo1d11s Catalyst (20+BaSis) Tempel,a Relsszasizh (lgasolme, point ture I cent temperature Method 27(274-283) 803 227 Synthetic 93 975 97. 0 45. 7 62(416-23) e52 155 (10 74 975 93.9 44.2 63(86-93) s52 975 95. 1 49. 9 27(43a 50) 540 75 979 99. 0 38.0 62(208-215) 876 97 975 95. 4 4s. 4 80(51-58) 97g 83 975 95. 1 50. 9 27-0(499-521 555 as 997 100+ 33.6 303'10489-512) 079 83 975 98. 9 42. a 301((410-473) 679 71 975 98. 6 39. e we 5924115 555 72 s71 99. 1 37. 2 211:(245-56) 777 7a 930 95. 2 5o. 4 35-0 148-71) 673 72 975 96. 4 45. 5 28-D (78-89) 555 71 994 97. 4 as. 5 28I(275 -98) 555 72 973 94. 5 42. o sew-54) s79 971 94. 9 52. 7 29J(537560) s42 75 981 97.0 43.7 2911 4ae452 863 55 978 94.9 41.5

1 Conversion of the portion of the feed stock above its 20% distillation temperature to lower boiling products and coke. 2 Synthetic catalyst is synthetically prepared silica alumina gel catalyst.

l Natural catalyst is acid treated bentonite clay catalyst.

9. The following comments are ofiered concerning the data in Table I, which lists the octane numbers produced when cracking various petroleum oils of different average boiling points.

Operations numbered 2 and 3, 8 and 9 illustrate the effect of changing the conversion level only. Operations 3, 5 and 6 show that when using the synthetic catalyst, the octane number stays about the same, provided the boiling level is above 800 F. Operations 7, 10, 13 and 14 show that operating temperature affects the octane number. Because of this, Operations 7 and 13 would show slightly lower (about 0.5-1.0) octane number if they are carried out at 975 F. reactor. temperature. Y

A comparison of the data in Operations 1-10 will show thensharp break in octane number obtained at about 800 F. average boiling point for synthetic catalyst. Operations 11- 15 show no such trend with natural catalyst.

A comparison of Operations 2, 3, 5 and 6 with Operation 15 shows that the natural catalyst produces about as high an octane number as the synthetic catalyst on high boiling petroleum oils.

A comparison of Operations 7 and 13, or a comparison of Operations and 14 shows that significantly higher octane numbers are obtained with the synthetic catalyst on low boiling petroleum oils. Operation 1 shOWS an intermediate boiling gas oil on synthetic catalyst which shows an intermediate octane number.

As a concrete example the following is given to show how the octane number of gasoline produced by-catalytic cracking may be increased. In the first operation, using syntheticsilica alumina catalyst, the gas oil had a boiling range (80%- 20% point) of 775 F. to 930 F. with an average boiling point of 852 F. The catalyst to oil ratio was about 10. The temperature during the cracking was about 975 F. About 50% by volume of the feed of gasoline having a final boiling point of 400 F. was obtained andthis gasoline had a CFRR octane number of 95.1;

In another example, using acid activated bentonite clay catalyst, the following is given. In this operation the gas oil-had a boiling range (80%-20% point) of 705 F. to'1050 F. with an average boiling point of 879 F. The catalyst to oil ratio was about 4. The temperature durin thecracking was about 971 F. About 53% by volume of the feed of gasoline having a final boiling point of 400 F. was obtained and this gasoline had a CFRR octane number of 94.9.

10 was about 167 F. The catalyst to oil ratio was. about 9 and the temperature during the cracking was about 975 F. The amount of gasoline produced was about 42% by volume of the feed and the gasoline had a CFRR octane number of 98.9.

In another operation, using the same type of feed stock as described in the previous example,v

and using acid treated bentonite clay catalyst, the gas oil was carefully fractionated so that the average boiling point was about 673 F. The boiling range (80%-20% point) of this feed stock was about 246 F. The .catalyst to oil ratio was about 6 and the temperature during the cracking was about975 F. The amount of gasoline pro-. duced was about 45% by volume of the feed and the gasoline had a CFRR octane number of 96;4.

In a third operation the feed stock was a similar type hydrocarbon oil and, contained the higher,

boiling constituents. 2e catalyst used was synthetic silica alumina gel catalyst. The higher boiling fraction had an average boiling point of about 803 F. and a. boiling range of about 227 F.

The catalyst to oil ratio was about 6 and the temperature of cracking was about 975 F. The amount of gasoline obtained was 46% by volume and the gasoline had a CFRR octane number of In another operation the feed stock was a similar type hydrocarbon oil and contained the higher boiling constituents but the catalyst used was acid treated bentonite clay catalyst. The higher boiling fraction had an average boiling point of about 777 F. and a boiling range of about 342 F.

The catalyst to oil ratio was about 3 and the temperature of cracking was about 930- F; The amount of gasoline obtained was 51% by volume and the gasoline, had a CFRR octane number of 95.2.

From the above operations it will be apparent that it is not as economical to crack high boiling gas oils with the more expensive synthetic catalyst when it is desired to make high octane gasoline.

In a more specific example, an East Texas hy-" drocarbon oil having a boiling range of about 430 F. to 1200 F. is fractionated into a 430 F. to 800 F. cut, which represents about 64% of the oil and an 800 F. to 1200 F. cut, which represents about 36% of the oil.

The separate cuts or fractions are catalytically' cracked at 950 F. and at conversion with different catalysts as follows:

Catalyst 1 Yield, Catalyst 1 Yield, Stock Octane Percent Octane Per cent No. No. 0

l 97. l 37. 3 94. 8 45.8 2 92. 1 49. 0 v 92. 6 58. 8 3 430l200 F 3 95.3 41. 5 4 93. 9 I 50.4 4 Blend oi Octane of 430-800 F. .with synthetic catalyst and 95.4 with ield of 44.8%

octan}; of 800-l200 F. with clay catalyst to give octane num r.

' Synthetic silica alumina catalyst Acid activated bentonite clay catalyst.

I Calculated Blend of l and 2. 4 Calculated Blend of 1 and 2.

In another example or operation the same type feed stock was used as above described in connection with the first operation but the catalyst used was synthetic silica alumina gel catalyst and the gas oil was carefully fractionated so that the average boiling point was about 679 F. The boiling range (%20% point) of this feed stock '75 alyst on the 800-1200 F. fraction than when usanot er ing the synthetic catalyst. Also, using the blend of the octane number of the fractions cracked with separate catalysts, the blend of. octanes will be 95.4 and the yield 44.8%,which shows that if the 'gasolines from the cracking steps are-blended, a higher percentage of a slightly higher octane number gasoline is obtained.

From the above data it will be seen that improved octane numbers are obtained by selecting the gas oilfraction to be catalytically cracked in the'presence of a synthetic cracking catalyst. In such a case, the gas oil fraction is selected to have an average boiling point below about 800 F. As the octane number decreases more'rapidly on the higher boiling stock when using synthetic catalyst than when usingthe clay catalyst, it is also within my'invention'to crack a lower boiling gas oilstock having an average boiling point'below about 800 F. with synthetic catalyst and cracking the higher boiling gas oil having an average boiling point above about 800 F. with clay catalyst to producegasoline having as high or a higher octane number than that produced when cracking a higher boiling gas oil stock with the expensive synthetic catalyst alone.

While I have disclosed my invention in connection with powdered catalyst in a bottom drawoiT unit, it is to be understood that my invention may also be used with powdered catalyst in an upflow unit and with fixed bed catalyst units where the catalyst remains in a vessel and is regenerated in the. same vessel after being used for some time. My invention may also be used with the moving bed type of operation in which the catalyst particles are inthe form of pellets or rods and are mechanically moved through the reaction vessel and then through'a separate regeneration vessel before being returned to the reaction vessel.

While I have shown one form of apparatus for carrying out my invention, it is to be understood that various changes and modifications may be made without departing from the spirit of my invention.

I claim:

.1. A process for catalytic cracking of hydrocarbons to produce higher yields of high octane gasoline which comprises separating a wide boiling range hydrocarbon oil into a low boiling fraction having an average boilinglpoint below about 800 F. (average boiling point being the temperature at which 80% of the stock boils off plus the temperature at which of the stock boils oil with the total divided by 2) and a higher boil ing fraction having an average boiling point above about 800 passing the low boiling fraction having an average boiling point below about 800 F. in the vaporphase through a first cracking zone containing powdered synthetic silica alumina catalyst with a catalyst to oil ratio by weight Of from 1 to and maintained at a temperature of about 975 F. to form high octane number gasoline having an octane number of at least 97 (CFR-Research Method), separating high octane gasoline from the cracked products, mixing a sufficient amount of powdered 'ho'tregenerated acid treated'bentonite-clay catalyst with said higher boiling fraction to vaporizethe higher boiling fractionand raise it to cracking temperature, passing the vaporized higher boiling fraction and catalyst through a second cracking zone maintained at a temperature of about 975 -'F. to form high octane number gasoline having "an octane number of about 95 (CFR-Research Method), separating high octane gasoline from the last-mentioned cracking step and' blendin'g high octane gasoline from'the first crackingstep with'high octane gasoline from the second cracking step to produce a. higher yield of=95 octane number gasoline than would be obtained by using a single catalyst.

2. Ap'rocess for catalytic cracking of hydrocarbons which comprises separating a wide boiling range hydrocarbon oil'into a low boiling fraction having an average boiling point below-about 800 F. (average boiling point being the temperature at which of the stock boils ofip'lus the temperature at which 20% of the stock boils "off with the total divided by 2) and a higher boiling fraction having an average. boiling point above about 800 F., passing the low boiling fraction having an average boiling point below about 800 F. in the vapor phase through a first cracking zone containing powdered synthetic silica alumina catalyst with a catalyst to oil "ratio by weight of from 1 to 40 and maintained'at-a temperature of about 975 F. to form high octane number gasoline, separating 'high octane gasoline from the cracked products, mixing a suflicient amount of powdered hot regenerated acid treated bentonite clay catalyst with said higher boiling fraction to vaporize the higher boiling fraction and raise it to cracking temperature, passing the vaporized higher boiling fractionand catalyst through a second cracking zone maintained at a temperature of about-975 F. to form gasoline having at least as high an octane number as would be obtained by cracking the higher boiling stock with the silica alumina catalyst but producing a higher yield of such gasoline, separating high octane gasoline from the last-mentioned cracking step and blending high octane gasoline from the first cracking step with high octane gasoline from the second cracking step to produce a higher yield of high octane gasoline than would be obtained if using the same "type of catalyst for both fractions of feed stock.

FORREST H. BLANDING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number .Name Date 2,230,552 Voorhies .1 Feb. 4, 1941 2,247,126 Hemminger June 24, 1941 2,308,557 Watson Jan. 19, 1943 2,309,137 Peterkin Jan. 26, 1943 2,387,088 Oblad et a1. Oct. 16, 1945 

1. A PROCESS FOR CATALYTIC CRACKING OF HYDROCARBONS TO PRODUCE HIGHER YIELDS OF HIGH OCTANE GASOLINE WHICH CCOMPRISES SEPARATING A WIDE BOILING RANGE HYDROCARBON OIL INTO A LOW BOILING FRACTION HAVING AN AVERAGE BOILING POINT BELOW ABOUT 800*F. (AVERAGE BOILING POINT BEING THE TEMPERATURE AT WHICH 80% OF THE STOCK BOILS OFF PLUS THE TEMPERATURE AT WHICH 20% OF THE STOCK BOILS OFF WITH THE TOTAL DIVIDED BY 2) AND A HIGHER BOILING FRACTION HAVING AN AVERAGE BOILING POINT ABOVE ABOUT 800*F. PASSING THE LOW BOILING FRACTION HAVING AN AVERAGE BOILING POINT BELOW ABOUT 800*F. IN THE VAPOR PHASE THROUGH A FIRST CRACKING ZONE CONTAINING POWDERED SYNTHETIC SILICA ALUMINA CATALYST WITH A CATALYST TO OIL RATIO BY WEIGHT OF FROM 1 TO 40 AND MAINTAINED AT A TEMPERATURE OF ABOUT 975*F. TO FORM HIGH OCTANE NUMBER GASOLINE HAVING AN OCTANE NUMBER OF AT LEAST 97 (CFR-RESEARCH METHOD), SEPARTING HIGH OCTANE GASOLINE FROM THE CRACKED PRODUCTS, MIXING A SUFFICIENT AMOUNT OF POWDERED HOT REGENERATED ACID TREATED BENTONITE CLAY CATALYST WITH SAID HIGHER BOILING FRACTION TO VAPORIZE THE HIGHER BOILING FRACTION AND RAISE IT TO CRACKING TEMPERATURE, PASSING THE VAPORIZED HIGHER BOILING FRACTION AND CATALYST THROUGH A SECOND CRACKING ZONE MAINTAINED AT A TEMPERATURE OF ABOUT 975*F. TO FORM HIGH OCTANE NUMBER GASOLINE HAVING AN OCTANE NUMBER OF ABOUT 95 (CFR-RESEARCH METHOD), SEPARATING HIGH OCTANE GASOLINE FROM THE LAST-MENTIONED CRACKING STEP AND BLENDING HIGH OCTANE GASOLINE FROM THE FIRST CRACKING STEP WITH HIGH OCTANE GASOLINE FROM THE SECOND CRACKING STEP TO PRODUCE A HIGHER YIELD OF 95 OCTANE NUMBER GASOLINE THAN WOULD BE OBTAINED BY USING A SINGLE CATALYST. 